In the art of orthopedic surgery, and particularly in spinal surgery, it has long been known to affix an elongated member, such as a plate or rod, to bones in order to hold them and support them in a given position. For example, in a procedure to fuse damaged, diseased, malformed, or otherwise abnormal vertebrae, the vertebrae are positioned in a corrected position by a surgeon. An elongated plate is placed adjacent to the vertebral bone, and bone anchors, such as specially-configured screws or bolts, are employed to secure the plate to the bones. With such anchors, placement is accomplished by drilling one or more holes in the bone(s) and threading the anchors into the holes. As examples, see U.S. Pat. No. 5,676,666 to Oxland et al., U.S. Pat. No. 5,613,967 to Engelhardt et al., and U.S. Pat. No. 5,603,713 to Aust et al. An anchor can be connected to the bone, as by threading into a vertebral hole, through a plate, or alternatively the plate can be placed in position over or around the anchor after the anchor is connected to the bone. The anchor and plate are then secured to each other to minimize or prevent relative movement. In this way, bones may be spinal held and/or supported in proper alignment for healing.
It has been found desirable for implant systems to have the capability for angular orientation of a bolt or other anchor in multiple planes relative to the elongated member or other fixation mechanisms of the implant system. Such features enable bone anchors to be placed at angles which are optimal for anchoring, thus reducing the chance of loosening, pull-out, or other movement of the anchors while not compromising the optimal positioning of the fixation plate.
Additionally, such systems alleviate awkwardness frequently found in spinal surgery due to uneven bone surfaces and the abnormality to be corrected and generally require less adjustment to the implant, rendering corrective surgery easier for the surgeon and less traumatic for the patient.
Various approaches have been used to achieve such multi-axial capability. For example, U.S. Pat. No. 5,735,853 to Olerud discloses an implant device in which a bone bolt can occupy different angular positions in relation to a plate by providing a compressible spherical collar which snap-fits around the bolt, which collar is rotatable and tiltable in a spherical opening in a plate insert. The compression fit of the bolt and collar within the plate can present difficulty in assembling the apparatus, particularly in a fluid-prevalent environment.
Another approach is shown in U.S. Pat. No. 5,304,179 to Wagner, which shows a bone screw fixed inside a bushing at an angle with respect to the longitudinal axis of the bushing. The bushing is rotatable within a portion of a connector angled with respect to the axis of the adjoining rod-based instrumentation. The connector is rotatable around the instrumentation axis. The Wagner system permits only discrete positions of a bone screw in three-dimensional space to be achieved, and the bushings add extra length and profile to the construct, as well as extra parts for the surgeon to handle and arrange.
A third approach is shown in U.S. Pat. No. 5,984,924 to Asher et. al., which shows a bone alignment system having an elongated bone alignment member sandwiched between two pairs of washers. Each such pair of washers have corresponding surfaces that mate together in a “ball and socket” configuration to potentially occupy a plurality of positions. When the shaft of a bone anchor extends through each washer pair, and also through an aperture of the elongated member, the washer pairs enable the shaft to be oriented at various angles relative to the elongated member. This approach also requires a plurality of small parts for handling and assembly during surgery. Further, since the washers in that system lie outside of the elongated member, they increase the thickness of the overall construct, with the attendant increase in the difficulty of use in a small surgical space and in the potential for patient discomfort.
As noted above, in placing such implants a surgeon is commonly required to reposition vertebrae so that a normal spinal curvature results from the surgery. In open surgical procedures, the surgeon may reposition vertebra(e) manually or may have tools to assist in the repositioning. Once the vertebrae are repositioned, implants can then be attached in order to hold the vertebrae in the desired position. Alternatively, it is also known to provide a rod that is pre-bent to approximate a normal spinal curvature and to provide hooks or screws that can hold the rod which attach to several vertebrae. With such apparatus, vertebrae can be repositioned by forcing the pre-bent rod into engagement with the hooks or screws that are already anchored in the vertebrae. Even with that method, however, additional tools such as a rod reducer are required. For example, to compress (i.e., push together) or distract (i.e., push apart) two vertebrae, it is known to use, among other relatively large tools, a scissors- or tongs-like device by squeezing or pulling apart on handles of such a tool; distal parts of the tool that contact vertebrae or devices attached to vertebrae will cause the distraction or compression.
Performing these tasks using traditional techniques and devices of open surgery has several undesirable features and consequences. Initially, such open surgery requires a long incision which leaves a relatively long and unappealing scar. Further, such surgery entails incision, retraction, and adjustment of numerous tissues in addition the spinal tissues. As a result, trauma to these tissues and resulting pain and possibility of infection are relatively high. Still further, a standard thoracotomy or other incision may expose only one apex of the spinal curve to be corrected, thus requiring additional long incisions or a longer initial incision in order to be able to fully treat the spine. Even where the apex of the spinal curve is adequately exposed and in good position relative to the thoracotomy for surgery, commonly adjacent vertebrae and intervertebral discs are not parallel to the exposure view provided by the incision, decreasing the effectiveness of instrumentation used to correct the abnormal curvature. For these reasons, an endoscopic, thoracoscopic, or other minimally-invasive approach is preferable.
Accordingly, there remains a need for a device that simplifies adjustment or repositioning of vertebrae, particularly when a minimally-invasive approach is used.